Natural coal is generally regarded as a non-renewable energy source in part because of the extreme amount of time needed for its formation. For instance, lignite coal requires thousands of years, and anthracite coal requires hundreds of millions of years for their respective formation. The conditions for formation of natural coal are believed to be achieved through sediment of plant and animal materials accumulated, pressurized and heated under increased bed depth.
Rapid oxidation or burning of natural coal releases toxic agents, such as heavy metals (e.g., mercury, uranium) co-deposited as part of the sedimentation formation process. The toxic content of natural coal has been both a significant health concern as well as a global environmental concern. The effect of released carbon dioxide into the atmosphere and its association with global warming present increasing problems associated with the use of natural coal. Increased regulation in the form of emissions controls and carbon emission levels is expected.
Synthetic or artificial coals have been produced from lignocellulosic sources, such as wood and peat. Schuhmacher et al., Fuel, 39(3) pp. 223-234 (1960) describes a process involving heating lignocellulosic material in water at temperatures between 225° C. and 390° C. generally under alkaline conditions to prepare artificial coal-like products. According to this process, gaseous by-products include carbon dioxide and the residue (“artificial coal”) obtained in decreasing yield with increasing temperature. Woody (lignocellulosic) and higher plants contain many kinds of cells with specific functions. Cellulosic, hemicellulose and lignin are products of specialized cells that provide structural stability and mechanical strength allowing for passage of water and nutrients throughout the various parts of the plant.
When compared on a per unit of mass basis, algae are known to be among the most photosynthetically efficient of all plants. Algae have even been employed as an “active scrubber” with sunlight to remove carbon dioxide via photosynthesis from industrial, carbon-dioxide waste streams associated with coal burning for electricity generation, as well as fermentation for fuel ethanol production. Microalgae are non-lignocellulosic single celled microorganisms composed of proteins, lipids, nucleic acids and carbohydrates.
Hydrothermal carbonization is a thermal decomposition process involving processing biomass in an aqueous system at moderate temperature and pressure for a period of time. The possibility of producing coal using algae and a hydrothermal carbonization process has been hypothesized in an abstract by company AlgoDyne Ethanol (Dec. 20, 2006). However, to Applicants' knowledge, a hydrothermal carbonization process has not previously been developed for the production of synthetic coal from algae or cyanobacteria nor has such a synthetic coal previously been produced. Thus, there exists a need in the energy resource field for algae-derived synthetic coal products, related by-products and processes for their production. There further exists a need for innovative processes utilizing natural biological materials as carbon neutral energy resources.